In the field of video surveillance, it is often desirable to capture an image of a vehicle license plate with a video camera to allow reading of the license plate information, for example, to facilitate identification or verification of the vehicle or its occupants. Under some conditions, it is necessary to capture an image of a vehicle license plate under relatively low light conditions. Automatic exposure control during license plate capture in low-light is made difficult by the very large dynamic range of lighting that typically exist under such conditions. Specifically, car headlights and taillights that may be significantly brighter than the license plate are typically combined with a poorly illuminated background that may be many times darker. In addition, motion of the license plate relative to the camera requires an auto-exposure algorithm to react quickly and complicates the exposure process since an exposure level must be selected to minimize image blur (a particular problem in low-light when a camera's exposure time might otherwise be longer). Although auto-exposure algorithms may allow for capture of license plate images during the day, under low light conditions they tend to overexpose headlights, taillights, and license plates that have been illuminated by an external infrared (IR) or visible light source.
Video surveillance cameras are currently available that are dedicated for license plate capture. These dedicated cameras make use of multiple snapshots, each with a different exposure time, to capture images of license plates. Out of the multiple snapshots captured by the dedicated surveillance camera, the hope is that one snapshot will have the correct balance of exposure and motion blur for capture of the license plate image. These cameras are dedicated license plate image capture devices and do not allow for non-license plate image capture related surveillance. Thus, it is necessary to add other video cameras to handle more general surveillance tasks.